Here is a screenshot of Charis SIL Compact in KF8 also showing the smallcaps. I think the line space looks good.

That looks great. I am half-tempted to replace Charis SIL Compact bold with the smallcaps bold. That should do the trick of having smallcaps chapter heading. I don't remember seeing bold inside a book - and if it happens out of tie blue moon, I am sure I won't mind it beeing smallcaps.